1. Field of the Invention
This invention relates to adherent polysiloxane compositions, products and articles of manufacture produced therefrom, and methods of use thereof. In particular, the invention relates to polysiloxane compositions that have the SiH.sub.3 functionality therein and can be cured to yield elastomeric gels capable of adhering to a variety of surfaces.
2. Description of Related Art
Silicone rubbers, gels, and elastomers are elastic materials typically prepared by crosslinking linear polyorganosiloxanes. Heinz-Herman, "Rubber, 1. Survey," Ullman's Encyclopedia of Industrial Chemistry, Vol. A23 (1993), VCH Publishers, Inc.; Osada, et al , "Intelligent Gels," Scientific American, (May, 1993) pages 82-87; Almdal, et al., Polymer Gels and Networks, (1993), Vol. 1, pages 5-17. These materials are valued for their resistance to environmental, chemical and biochemical degradation, and for the retention of their tensile and other physical properties even after exposure to extremely high or low temperatures for long periods. Uses for silicone elastomers include encapsulants for electronic components, breast prostheses, waterproof and rust-proof coatings on metals, non-stick coatings on medical devices, dental impression gels and shock absorbing cushions in footwear and automobiles. Usually, it is essential that the polysiloxane composition have adequate cohesive strength as well as excellent adhesive strength when in contact with various substrates.
Gels, elastomers and rubbers are differentiated by the extent of crosslinking within the siloxane network and by hardness and elasticity. That is, hardness and elasticity are a function of crosslinking, as well as the specific raw materials used (e.g., shorter molecules lead to less elasticity). One quantitative measure of this difference is the modulus or resistance to deformation. Modulus is measured in units of force per unit area; for example, modulus units can be newtons per square meter, N/m.sup.2, also called a Pascal, Pa. Rubbers typically have moduli of about 10.sup.5 -10.sup.6 Pa, whereas gels have moduli of about 10.sup.2 -10.sup.5 Pa. The crosslinked polysiloxane compositions of this invention are silicone gels and rubbery elastomers.
Crosslinking, also referred to as curing or vulcanization, can be effected with organic peroxides, high energy radiation or organometallic catalysts. Heat is often applied to initiate the peroxide and metal-catalyzed crosslinking reactions. The method selected depends on factors such as the composition of the polyorganosiloxane, the time and temperature required for curing and the cost of manufacturing. Crosslinking with organometallic catalysts occurs either by addition cure or condensation cure.
Typically, addition cure is catalyzed by a divalent or zerovalent platinum compound as described in U.S. Pat. Nos. 3,419,593 and 3,775,452. Addition cure is characterized by the hydrosilation reaction of an unsaturated linkage such as, for example, vinyl, alkynyl or allyl by a hydrosiloxane group, Si--H, to yield Si--C bonds. Condensation cure is usually catalyzed by tin or titanium catalysts, examples of which are disclosed in U.S. Pat. Nos. 3,186,963 and 3,708,467. In condensation cure, silanol groups combine to produce Si--O--Si linkages and water. The equations below illustrate both processes.